MXPA05003813A

MXPA05003813A - Process for production of a carboxylic acid/diol mixture suitable for use in polyester production.

Info

Publication number: MXPA05003813A
Application number: MXPA05003813A
Authority: MX
Inventors: Lin Robert
Original assignee: Eastman Chem Co
Priority date: 2002-10-15
Filing date: 2003-10-09
Publication date: 2005-06-08
Also published as: JP2006503087A; RU2330014C2; BRPI0314833B1; MY138840A; BR0314833A; US7339072B2; KR20050055764A; PT1551788T; CA2498621A1; PL377385A1; KR101288685B1; US7276625B2; TW200418789A; WO2004035515A1; AR041608A1; EP1551788B1; US20050154179A1; AU2003277321A1; EP1551788A1; RU2005114535A

Abstract

In this invention, a process is provided by which a carboxylic acid/diol mixture suitable as starting material for a polyester production is obtained from a decolorized carboxylic acid solution without isolation of a substantially dry carboxylic acid solid. More specifically, in this invention, a process is provided by which a terephthalic acid/ethylene glycol mixture suitable as starting material for a polyester production is obtained from a decolorized terephthalic acid solution without isolation of a substantially dry terephthalic acid solid.

Description

PROCESS FOR THE PRODUCTION OF A MIXTURE OF CARBOXYLIC ACID / DIOL ADEQUATE FOR USE IN POLYESTER PRODUCTION FIELD OF THE INVENTION The present invention relates to a process by which a mixture of carboxylic acid / diol is obtained from a decolorized carboxylic acid solution without isolation of a substantially dry solid carboxylic acid. More specifically, the present invention relates to a process by which a mixture of terephthalic acid / ethylene glycol suitable as an initial material for the production of polyester is obtained from a decolorized solution of terephthalic acid without isolation of a substantially dry solid terephthalic acid. .

DESCRIPTION OF THE INVENTION Thermoplastic polyesters are polymer growth stages that are useful when they are made of high molecular weights. The first step in a common method for producing a polyester such as polyethylene terephthalate (PET) is an esterification or exchange ester phase wherein a diacid (typically terpetalic acid) reacts with an appropriate diol (typically ethylene glycol) to give an (hydroxyalkyl) ester and some linear oligomers. Water is developed in this phase and is usually removed by fractional distillation. In accordance with the aim of making polyethylene terephthalate and other polyesters, much of the patent literature is devoted to the description of processes for preparing mixtures of terephthalic acid / ethylene glycol suitable as starting material. In general, these inventions describe specific combinations of mixtures of combinations with a purified solid terephthalic acid and liquid ethylene glycol as starting materials. Additionally, this is a substantial body of literature dedicated to producing a purified terephthalic acid in the powder form that is suitable for use in the production of PET. The objective of this invention is to describe a process by which a mixture of terephthalic acid / ethylene glycol suitable as initial material for the production of polyester is obtained from a decolorized solution of terephthalic acid without isolation of a substantially dry solid terephthalic acid. A number of processes for producing purified solid terephthalic acid have been developed and are commercially available. Usually, purified solid terephthalic acid is produced in a multi-stage process in which a crude terephthalic acid is produced. The crude terephthalic acid does not have sufficient quality for direct use as initial material in commercial PET. In contrast, crude terephthalic acid is usually refined to purify solid terephthalic acid. The liquid oxidation phase of p-xylene produces crude terephthalic acid. The crude terephthalic acid is dissolved in water and hydrogenated for the purpose of converting 4-carboxybenzaldehyde to p-toluidic acid, which is a more water-soluble derivative, and for the purpose of characteristically converting yellow compounds to colorless derivatives. Any 4-carboxybenzaldehyde and p-toluidic acid in the final purified terephthalic acid product is particularly detrimental to polymerization processes when they act as a dividing chain during the condensation reaction between terephthalic acid and ethylene glycol in the production of PET. Typical purified terephthalic acid contains less than 25 parts per million (ppm) of 4-carboxybenzaldehyde and less than 150 ppm p-toluidic acid at a basis weight. Crude terephthalic acid typically contains at a basis weight from 800 to 7,000 parts per million (ppm) of 4-carboxybenzaldehyde and 200 to 1,500 ppm of p-toluidic acid as the main impurities. Crude terephthalic acid also contains lower amounts, 20-200 ppm range, of yellow aromatic compounds that have the structures of benzyl, fluoranone, and / or anthraquinone, which are yellow compound characteristics as impurities resulting from side reactions of coupling occurred or during the oxidation of p-xylene. This is necessary, to purify crude terephthalic acid when it is used as an initial material to produce polyester fiber, which requires a purified terephthalic acid as an initial material. As a typical purification process, it comprises adding water to the crude terephthalic acid to form a crude solution of tephthalic acid, which is heated to dissolve the crude terephthalic acid. The crude solution of terephthalic acid is then passed to a zone of the reactor in which the solution is in contact with hydrogen in the presence of a heterogeneous catalyst at temperatures of 200 ° C to 375 ° C. This reduction step converts the bodies of various colors present in the crude terephthalic acid to colorless products. The main impurity, 4-carboxybenzaldehyde, is converted to p-toluidic acid. Typical crude terephthalic acid contains excessive amounts of both -carboxybenzaldehyde and p-toluidic acid at a basis weight. Therefore, to achieve less than 25 ppmmp of 4-carboxybenzaldehyde and less than 150 ppmmp of p-toluidic acid in the purification of terephthalic acid, mechanisms are required to purify crude terephthalic acid and remove contaminants. The subsequent separation and isolation of the purified terephthalic acid can be achieved via a wide variety of separation methods including crystallization, centrifugation, filtration, extraction and combinations of those followed by drying. These processes are described in U.S. patents. 4,500,732; 5,175,355; and 5,583,254; all of which have been incorporated here by reference. This is necessary to develop a separation step due to the nature of the feed stream of the crude terephthalic acid for the hydrogenation process. A number of processes have been developed to produce a solid terephthalic acid purified from crude terephthalic acid. In general, the common characteristics between these processes are as follows: Step (1) is decolorization of crude terephthalic acid usually via hydrogenation treatment in an aqueous medium, - Step (2) is purification / separation of terephthalic acid from partial oxidation products usually via fractional crystallization followed by an exchange liquor with water free of contaminant; and Step (3) is the production of a solid product purified from terephthalic acid with the consequent material with manageable properties usually via crystallization of terephthalic acid followed by drying of purified terephthalic acid from water. The resulting powder of purified terephthalic acid together with ethylene glycol are starting materials in the production of polyesters specifically PET. Because of the difficulty in handling, mixing, and dissolving solid terephthalic acids, purified solid terephthalic acid is usually mixed with ethylene glycol to form a paste prior to introduction into a sterilization reactor system. In the present invention, a novel process has been discovered resulting in fewer steps than the processes currently employed. The primary use of the invention is the reduction of capital and operating costs associated with the isolation of the powdered terphthalic acid. In conventional access for the production of terephthalic acid, post-hydrogenation of aqueous solution is carried to a series of crystallized vessels for the purpose of purifying terephthalic acid by crystallization and for the purpose of obtaining a uniform particle distribution size for a good fluidity of the purified terephthalic powder. In addition, the p-toluidic acid mother liquor contaminated from the crystallization process must be removed before the drying step to isolate the purified terephthalic powder.

In one embodiment of the present invention, the crude solution of terephthalic acid with low concentration of p-toluidic acid and 4-carboxybenzaldehyde is hydrogenated to form a decolorized solution of terephthalic acid. Starting with crude terephthalic acid with low concentrations of p-toluidic acid and 4-carboxybenzaldehyde eliminates the need for the separation of p-toluxic acid mother liquor contaminated with terephthalic acid. Therefore, the decolorized terephthalic acid solution can be directly combined with ethylene glycol in an esterification zone to produce a mixture of terephthalic acid / ethylene glycol. By deviation from conventional processes to produce a purified terephthalic acid powder, the need for the equipment necessary to purify and isolate the purified terephthalic powder is eliminated. Another surprising and apparently contradictory aspect of the invention is the benefit of adding large amounts of water to the esterification reaction of starting materials. This is directly contrary to the accepted procedures of esterification. The esterification reaction: RCOOH + R'OH? RCOOR '+ ¾0 is generally not complete. The water formed in the course of the reaction tends to react with the aster to hydrolyze it; for example to regenerate the original alcohol and the acid. In order to handle the reaction to the ester, those skilled in the art eliminate water from the system by a variety of methods such as distillation or dehydration with a hydrophilic compound. In accordance with conventional esterification methods, it is non-intuitive to add large amounts of water to the acid / alcohol starting materials.

BRIEF DESCRIPTION OF THE INVENTION The present invention relates to a process by which a mixture of carboxylic acid / diol is obtained from a decolorized carboxylic acid solution without isolation of a substantially dry solid carboxylic acid. More specifically, the present invention relates to a process for the production of a mixture of a terephthalic acid / ethylene glycol suitable as a feed stream for the commercial production of PET. The resulting process has fewer steps than the processes currently used and can be operated at lower operating costs and is built at low capital costs. Specifically, the present invention incorporates a direct displacement of water with the ethylene glycol step followed by the hydrogenation treatment of the crude terephthalic acid. The displacement step mode eliminates the need to isolate a purified solid tephthalic acid thereby eliminating the need for crystallization, solid-liquid separation, and solids that are normally occupied by equipment found in commercial processes of purified terephthalic acid. It is an object of this invention to provide a process for the production of a carboxylic acid / diol mixture without isolation of a substantially dry solid carboxylic acid. It is another object of this invention to provide a process for the production of a terephthalic acid / ethylene glycol mixture without isolation of a substantially dry solid tephthalic acid. It is another object of this invention to provide a process for the production of a mixture of terephthalic acid / ethylene glycol without the isolation of a substantially dry solid terephthalic acid by vaporizing water from a decolorized solution of terephthalic acid without enthalpy supply by ethylene glycol in an esterification reactor. It is another object of this invention to provide a process for the production of a mixture of terephthalic acid / ethylene glycol without the isolation of a substantially dry solid tephthalic acid by removal of water from a decolorized solution of terephthalic acid through the use of liquid solid displacement such as centrifuges, filters or cyclones.

In a first embodiment of this invention, a process for the production of a carboxylic acid / diol mixture is provided, the process comprises adding a diol to a decolorized solution of carboxylic acid in the reactor esterification zone to remove a portion of the water for forming the carboxylic acid / diol mixture; wherein the carboxylic acid and diol subsequently react in the esterification zone to form a hydroxyalkyl ester stream. Typically, the carboxylic acid is selected from a group consisting of terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, and mixtures thereof. In another embodiment of this invention, a process for the production of a carboxylic acid / diol mixture is provided, the process comprises the following steps: (a) mixing a crude carboxylic acid powder with water in a mixing zone to form a solution crude carboxylic acid; wherein the carboxylic acid is selected from a group consisting of terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, and mixtures thereof (b) decolorize the crude carboxylic acid solution in a reactor zone to produce a decolorized solution of carboxylic acid; (c) optionally, vaporizing the decolorized carboxylic acid solution in a vaporization zone to remove a portion of water from the decolorized carboxylic acid solution; and (d) adding a diol to the decolorized carboxylic acid solution in an esterification zone of the reactor to vaporize a portion of the water to form the carboxylic acid / diol mixture; wherein the carboxylic acid and diol subsequently react in the esterification zone to form a hydroxyalkyl ester stream. In another embodiment of this invention, a process for producing a mixture of terephthalic acid / diol is provided, the process comprising vaporizing a decolorized solution of terephthalic acid with a diol in an esterification zone of the reactor to remove a portion of the water to form the terephthalic acid / diol mixture; in the acid, terephthalic and diol subsequently reacts in the esterification zone to form a hydroxyalkyl ester stream.

In another embodiment of the invention, a process for producing a terephthalic acid / diol mixture is provided, the process comprises the following steps: (a) mixing the crude terephthalic acid powder with water in a mixing zone to form a crude solution of terephthalic acid; (b) decolorizing the crude solution of terephthalic acid in a zone of the reactor to form a decolorized solution of the terephthalic acid. (c) Optionally, vaporize the decolorized solution of terephthalic acid in a vaporization zone to remove a portion of water from the terephthalic aqueous solution; and (d) adding a diol to the decolorized terephthalic acid solution in an esterification zone of the reactor to remove a portion of water to form the terephthalic acid / diol mixture, in which the terephthalic acid and diol subsequently reacts from a stream of hydroxyalkyl ester. In another embodiment of this invention a process for producing a carboxylic acid / diol mixture is provided; the process comprises removing a portion of water contaminated with p-toluidic in an aqueous mixture of terephthalic acid by adding a diol in a liquor removal zone to produce the carboxylic acid / ethylene glycol mixture. In another embodiment of this invention, a process for producing a carboxylic acid / diol mixture is provided, the process comprises the following steps: (a) mixing a crude carboxylic acid powder with water in a mixing zone to form a crude solution of carboxylic acid; (b) decolorize crude carboxylic acid in a zone of the reactor to produce a decolorized carboxylic acid solution. (c) crystallize the decolorized carboxylic acid solution in a crystallization zone to form an aqueous mixture of terephthalic acid; and (d) removing a portion of the contaminated water in the aqueous mixture of terephthalic acid by adding a diol in a liquor removal zone to produce the carboxylic acid / diol mixture. In another embodiment of this invention, a process for producing a terephthalic acid / ethylene glycol mixture is provided, the process comprising removing a portion of water contaminated with p-toluidic in an aqueous mixture of terephthalic acid by the addition of a diol in a removal zone. of liquor to produce the mixture teref alico acid / diol. In another embodiment of this invention, a process for producing a terephthalic acid / ethylene glycol mixture is provided, the process comprises the following steps: (a) mixing a crude terephthalic acid powder with water in a mixing zone to form a crude solution of terephthalic acid; (b) decolorizing the crude solution of terephthalic acid in a zone of the reactor to form a decolorized solution of terephthalic acid; (c) crystallizing the decolorized terephthalic acid solution in a crystallization zone to form an aqueous mixture of terephthalic acid; and (d) removing a portion of water contaminated with toluene in the aqueous mixture of terephthalic acid by the addition of a diol in a liquor removal zone to produce the terephthalic acid / diol mixture. These objectives and other objectives; they will be more obvious to others with ordinary experience in the field after reading this description. BRIEF DESCRIPTION OF THE FIGURES Figure 1 illustrates one embodiment of this invention. A process is provided using powdered carboxylic acid to produce a carboxylic acid / diol mixture with the subsequent reaction of carboxylic acid and diol to form a hydroxyalogyl ester stream. Figure 2 illustrates an alternative embodiment of this invention. A process is provided using a terephthalic acid powder to produce a terephthalic acid / diol mixture with the subsequent reaction of terephthalic acid and diol to form a hydroxyalkyl ester stream. Figure 3 illustrates another alternative embodiment of this invention. A process is provided which utilizes a powdered carboxylic acid to produce a carboxylic acid / diol mixture. Figure 4 illustrates yet another embodiment of this invention. A process is provided where a crude terephthalic acid powder is used to produce a terephthalic acid / diol mixture.

DETAILED DESCRIPTION OF THE FIGURES In the first embodiment of this invention a process for producing a carboxylic acid / diol mixture, the process comprises the addition of a diol to a decolorized solution of carboxylic acid in an esterification zone of the reactor to remove a portion of water to form the carboxylic acid / diol mixture; wherein the carboxylic acid is selected from a group consisting of terephthalic acid, isophthalic acid, naphthalic dicarboxylic acid, and mixtures thereof; wherein the carboxylic acid and diol subsequently react in the esterification zone from a hydroxyalkyl ester stream. The esterification zone of the reactor, the decolorized carboxylic acid solution and a process for producing the decolorized carboxylic acid solution is subsequently described in a second embodiment of this invention.

In the second embodiment of this invention a process for producing a carboxylic acid / diol mixture is provided as shown in Figure # 1. Step (1) comprises mixing a crude carboxylic acid powder in conduit 105 with water in conduit 115 in a mixing zone 110 to form a crude solution of carboxylic acid in conduit 120; typically, the carboxylic acid is selected from a group consisting of terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, and mixtures thereof. The mixing of the crude carboxylic powder in the conduit 105 with water in the conduit 115 in the mixing zone 110 can be achieved by any means known in the art. The mixing zone 110 may be any container or equipment capable of mixing the crude carboxylic acid powder. The temperature and pressure of the mixing zone 110 is that which is sufficient to properly mix the raw carboxylic acid powder in conduit 105 with water in conduit 115. Typically, the crude carboxylic acid powder in conduit 105 with water in conduit 115 in mixing zone 110 at a concentration of 15-35% by weight. Step (2) the raw carboxylic acid solution in the duct 120 is decolorized in a zone of the reactor 125 to produce a decolorized carboxylic acid solution 135. The decolorization of the crude carboxylic acid solution in the duct 120 can be achieved by any half known in art. Preferably, the discoloration can be achieved by reacting the crude carboxylic acid solution in conduit 120 with hydrogen in conduit 130 in the presence of a catalyst in a zone of reactor 125 to produce a decolorized carboxylic solution. For reactor zone 125, there are no special limitations in the form or construction thereof, subject to an arrangement that allows the supply of hydrogen in conduit 130 to effect intimate contact of the crude carboxylic acid solution in the conduit 120 with the catalyst in the reactor zone 125. Typically, the catalyst is usually a single metal of Group VIII or combination of Group VIII metals. Preferably, the catalyst is selected from a group consisting of palladium, ruthenium, rhodium and combinations thereof. More preferably, the catalyst is palladium. Typically, the catalyst is preferably supported on porous carbon. Reactor zone 125 comprises a hydrogenation reactor operating at a temperature and pressure sufficient to hydrogenate the characteristically yellow compounds in the crude carboxylic acid solution in conduit 120. By hydrogenation treatment, the characteristically yellow compounds in the crude solution of carboxylic acid are converted into colorless derivatives. The color b * of a decolorized carboxylic acid solution in conduit 135 is between 0.5 to 4. Preferably the color b * in the carboxylic solution in conduit 135 is between 0.5 to 2.0. More preferably the color b * in the carboxylic solution in conduit 135 is between 0.5 to 1.05. The b * is one of the three attributed colors measured in a refle-base spectroscopic instrument. The color can be measured by any device known in the art. An Ultrascan XE Hunter instrument is typically the measuring device. Positive readings mean the degree of yellow (or absorbance of blue), while negative readings mean the degree of blue (or absorbance of yellow). The hydrogen in line 130 is fed at a sufficient rate to convert the characteristically yellow compounds to the crude carboxylic mixture in line 120 for colorless derivatives; wherein the color b * is between 0.5 to 4.0 in the decolorized carboxylic acid solution in conduit 135. Step (3) optionally comprises vaporizing the decolorized carboxylic acid solution 135 in a vaporization zone 145 to remove a portion of water of the decolorized solution of carboxylic acid in the conduit 135. The vaporization of the aqueous carboxylic solution 135 can be achieved by any means known in the art. Typically, a container or a plurality of containers are used to achieve vaporization. In the vaporization zone 145, water and residual hydrogen can be removed as a vapor path in line 150. The vaporization vessel (s) operates at a temperature sufficient to remove a portion of the water. Alternatively, vaporization zone 145 can be omitted as indicated by conduit 140. Step (4) comprises, adding a diol in conduit 170 for the decolorized carboxylic acid solution in conduit 155. A portion of the water via conduit 165 is removed from an esterification zone of reactor 160 to form the carboxylic acid / diol mixture in the esterification zone of reactor 160. The carboxylic acid and diol subsequently react to form a hydroxyaluyl ester 175 stream. The hydroxyalkyl ester 175 stream comprises a compound hydroxyalkyl ester. The diol in line 170 is introduced in such a manner as to displace the water as the dominant mixed liquid. This can be achieved by introduction of diol via conduit 170 as a saturated liquid at a temperature which is sufficient to vaporize the water. Preferably, the diol in line 170 is introduced as a saturated or superheated steam. The diol in line 170 is selected from the group consisting of ethylene glycol, diethylene glycol, n-butylene glycol, i-butylene glycol, n-propylene glycol, 1,4-butanediol, cyclohexanedimethanol, and mixtures thereof. Preferably, the diol in line 170 is ethylene glycol.

Alternatively, an external heat source can be used to introduce enough enthalpy to vaporize the water, which exists via conduit 165. The hydroxyalkyl ester stream exists via conduit 175. The esterification zone of reactor 160 operates at a temperature that is sufficient to produce hydroxyethyl from the carboxylic acid mixture. The esterification zone of the reactor 160 comprises an esterification reactor. The esterification can be achieved by any means known in the art. In a third embodiment of this invention a process for producing a terephthalic acid / diol comprises vaporizing a decolorized solution of terephthalic acid with a diol in an esterification zone of the reactor to remove a portion of the water to form the terephthalic acid / diol mixture; wherein the terephthalic acid and diol subsequently react in the esterification zone to form a hydroxyalkyl ester stream. The reactor esterification zone, the decolorized terephthalic acid solution and a process for producing the decolorized terephthalic acid solution is subsequently described in a fourth embodiment of this invention. In the fourth embodiment of this invention a process for producing a terephonic acid / diol mixture is provided as shown in Figure # 2. Step (1) comprises mixing a crude terephthalic acid powder in line 205 with water in line 215 in a mixing zone 210 to form a crude solution of terephthalic acid in line 220. Mixing of the raw terephthalic powder in line 205 with water in line 215 can be achieved by any means known in the art. The initial feed material is the crude terephthalic acid powder in line 205 with some specific physical characteristics that differ from crude terephthalic acid described in U.S. Pat. 5,095,146 and U.S. Pat. 5,175,355, incorporated herein by reference. Specifically, the total amount of p-toluidic acid and 4-carboxybenzaldehyde in the crude terephthalic acid powder in line 205 is less than 900 ppm in a basis weight, preferably, less than 500 ppm, and more preferably, less than 250 ppm. . Another feature of the terephthalic raw powder in line 205 is the color as measured by b * is less than 7. Preferably, the color measured by b * is between 4 and 6. The mixing zone 210 can be any container or equipment capable of mixing the crude terephthalic acid powder in the conduit 205 with water in conduit 215. The crude terephthalic acid in powder in the conduit 205 is mixed in water in conduit 215 in the mixing zone 210 to produce the crude terephthalic acid solution in the conduit 220. The crude terephthalic acid and water are heated in a mixing zone 210 at a temperature of 230 ° C or higher to dissolve the crude terephthalic acid powder in the conduit 205 in the mixing zone 210 to produce the crude solution of terephthalic acid in line 220. Preferably, the crude terephthalic mixture in the mixing zone 210 is heated to a temperature in the range of 240 ° C to 300 ° C. The pressure of the mixing zone is 900 psia to 1400 psia to dissolve crude terephthalic acid powder in conduit 205 in the mixing zone 210. Generally, the concentration of crude terephthalic acid in the crude solution of terephthalic acid is 15%. 30% by weight, preferably, 20 to 30% by weight. Step (2) is the decolorization of the crude terephthalic acid solution in line 220 in a reactor zone 225 to form a decolorized solution of terephthalic acid in line 235. The decolorization of the raw solution of terephthalic acid in line 220 can be achieved by any means known in the art. Preferably, the decolorization can be achieved by reacting the crude solution of terephthalic acid in line 220 with hydrogen in line 230 in the presence of a catalyst in a zone of the reactor 225 to produce a decolorized solution of terephthalic acid. For reactor zone 225, there are no special limitations in the form or construction thereof, subject to an arrangement that allows supply of hydrogen in the conduit 230 to effect the intimate contact of the crude solution of terephthalic acid in the conduit 220 with the catalyst in the region of the reactor 225. Generally, the catalyst is usually a single metal of Group VIII or a combination of Group VIII metals. Preferably, the catalyst is selected from a group consisting of palladium, ruthenium, rhodium and combination thereof. More preferably, the catalyst is palladium. Typically, the catalyst is supported, preferably in porous carbon. The reactor zone 225 comprises a hydrogenation reactor which operates at a temperature of 230 ° C or higher. Preferably, the hydrogenation reactor operates in the range of 240 ° C to 300 ° C. The hydrogenation reactor operates at a pressure of 900 psia at 1400 psia and at a hydrogen partial pressure of at least 100 psia. Preferably, the partial pressure of hydrogen is in the range of 100 to 300 psia. By hydrogenation treatment, the characteristically yellow compounds in the crude solution of terephthalic acid are converted to colorless derivatives. In addition, the reactor zone converts a portion of 4-carboxybenzaldehyde to p-toluidic acid. The hydrogen in line 230 is fed at a rate of at least 1.5 times the molar ratio necessary to convert the 4-carboxybenzaldehyde in the crude solution of terephthalic acid in line 220 to p-toluidic acid. Preferably, the hydrogen 230 is fed at a rate of at least 2.0 times the molar ratio necessary to convert the 4-carboxybenzaldehyde in the crude solution of terephthalic acid 220 to p-toluic acid. The color b * is between 0.5 to 4 in the decolorized solution of terephthalic acid in duct 235. Preferably the color b * in the decolorized solution of terephthalic acid in duct 235 is between 0.5 to 1.5. Step (3) optionally comprises vaporizing the decolorized terephthalic acid solution 235 in a vaporization zone 245 to remove a portion of the water 250 from the aqueous terephthalic acid solution 235. The vaporization of the terephthalic aqueous solution 235 can be achieved by any half known in art. Typically, a container or a plurality of containers are used to achieve vaporization. In the vaporization zone 245, water and residual hydrogen can be removed as a vapor via line 250. The vaporization vessel (s) operates at a temperature of 150 ° C or higher. Preferably, the vaporization vessel (s) operates in a range of 155 ° C to 260 ° C. The vaporization vessel (s) operates under a pressure of 74 psia at 1400 psia. Specific ranges of operation vary depending on the amount of water removed via conduit 250. Alternatively, vaporization zone 245 may be omitted as indicated by conduit 240.

Step (4) comprises adding a diol in conduit 270 of the decolorized terephthalic acid solution in conduit 255 in an esterification zone of reactor 260 to remove a portion of the water via conduit 265 to form the a terephthalic acid / diol mixture. in the esterification zone of reactor 260. The carboxylic acid and diol react to form a hydroxyalkyl ester stream 275. The hydroxyalkyl ester stream 275 comprises a hydroxyalkyl ester compound. The diol in line 270 is introduced in such a way as to displace the water as the dominant mixed liquid. This can be achieved by introducing a diol via line 270 as a saturated liquid in a temperature range of 150 to 300 ° C. Preferably, the diol in line 270 is introduced as a saturated or superheated steam in the temperature range of 150 to 300 ° C in a form with sufficient enthalpy to evaporate the water to exit via line 265. The diol in the line 270 is selected from the group consisting of ethylene glycol, diethylene glycol, n-butylene glycol, i-butylene glycol, n-propylene glycol, 1,4-butanediol, cyclohexanedimethanol, and mixtures thereof. Preferably, the diol in line 270 is ethylene glycol. Alternatively, an external heat source can be used to introduce enough enthalpy to vaporize the water, which exits via conduit 265. The mixture of the hydroxyalkyl ester stream exits via conduit stream 275. The esterification zone of the reactor 260 operates at a temperature greater than 240 ° C. Preferably the esterification zone of reactor 260 operates in the temperature range of 260 ° C to 280 ° C. The esterification zone of the reactor 260 operates under a pressure of 40 psia at 100 psia to effect the esterification of the terephthalic acid / diol 275 mixture to produce a terephthalic acid hydroxyethyl ester. In a fifth embodiment of this invention, a process for producing a carboxylic acid / diol mixture comprises removing a portion of contaminated water in an aqueous mixture by adding a diol in a liquor removal zone to produce the carboxylic acid mixture. diol The liquor removal zone, the aqueous mixture and a process for producing the aqueous mixture are subsequently described in a sixth embodiment of this invention. In the sixth embodiment of this invention, a process for producing a carboxylic acid / diol mixture is provided as shown in Figure # 3. Step (1) comprises mixing a crude carboxylic acid powder in conduit 305 with water in conduit 315 in a mixing zone 310 to form a crude solution of carboxylic acid in conduit 320. Mixing of the crude carboxylic powder in conduit 305 with water in conduit 315 in the mixing zone 310 can be achieved by any means known in the art. The initial feed material is the crude carboxylic acid powder in line 305. Typically, the carboxylic acid is selected from a group consisting of terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, and mixtures thereof. The mixing zone 310 can be any container or equipment capable of mixing the crude carboxylic acid powder in conduit 305 with water in conduit 315. The crude carboxylic acid powder in conduit 305 and water in conduit 315 in the mixing zone 310 is heated to a temperature sufficient to dissolve the crude carboxylic acid powder in conduit 305 in the mixing zone 310 to produce the crude solution of carboxylic acid in conduit 320. The pressure of the mixing zone 310 is at a sufficient pressure for dissolving the crude carboxylic acid powder in conduit 305 in the mixing zone 310. Generally, the concentration of the crude carboxylic acid in the crude carboxylic acid solution is 15% to 35% by weight. Step (2) is decolorized from the crude carboxylic acid solution in conduit 320 in a zone of reactor 325 to form a decolorized carboxylic acid solution in conduit 330.

The decolorization of the crude solution of carboxylic acid in conduit 320 can be achieved by any means known in the art. Preferably, the decolorization can be achieved by reaction of the crude solution of carboxylic acid in conduit 320 with hydrogen in conduit 330 in the presence of a catalyst in a zone of reactor 325 to produce a decolorized solution of carboxylic acid. For reactor zone 325, there are no special limitations on the form or construction thereof, subject to an arrangement that allows hydrogen to be supplied in conduit 330 to make intimate contact of the crude carboxylic mixture 320 with the catalyst in the zone of the reactor. reactor. Typically, the catalyst is usually a single metal Group VIII or combination of metals Group VIII. Preferably, the catalyst is selected from a group consisting of palladium, ruthenium, rhodium and combination thereof. More preferably, the catalyst is palladium. Typically the catalyst is supported, preferably in porous carbon. Reactor zone 325 comprises a hydrogenation reactor operating at a temperature sufficient to convert the characteristically yellow compounds in the raw solution of carboxylic acid 320 to colorless derivatives. The color b * in the decolorized solution of carboxylic acid in conduit 335 is between 0.5 to 4. Preferably the color b * of the carboxylic acid solution in conduit 335 is between 0.5 to 2. More preferably the b * color in the decolorized solution of carboxylic acid in conduit 335 is between 0.5 to 1.5. The hydrogen in line 330 is fed at a sufficient rate to convert the characteristically yellow compounds in the crude carboxylic mixture in line 320 to colorless derivatives; wherein the color b * is between 0.5 to 4 in the decolorized carboxylic acid solution in conduit 335. Step (3) comprises crystallizing the decolorized carboxylic acid solution in conduit 335 in a crystallization zone 345 to form an aqueous mixture in the conduit 355. The crystallization zone 345 comprises a container or a plurality of containers capable of removing water from the decolorized carboxylic acid solution in conduit 335 to produce an aqueous mixture in conduit 355. Typically, the containers comprise at least one crystallizer. Examples of such systems can be found in U.S. patents. 5,567,842 and 3,931,305, incorporated herein by reference. Generally, the aqueous mixture in conduit 355 has a carboxylic acid concentration of from 10 to 60 weight percent. The temperature range of the carboxylic acid solution in the crystallization zone 345 is such that it is sufficient to remove a portion of water. Step (4) comprises removing a portion of contaminated water via conduit 365 in aqueous mixture 355 by adding a diol in conduit 370 in a liquor removal zone 360 to produce a carboxylic acid / diol mixture in conduit 375. The purpose of liquor removal in zone 360 is to replace contaminated water with a diol in line 370. Contaminated water comprises water and typical contaminants. The diol in line 370 is selected from the group consisting of ethylene glycol, diethylene glycol, n-butylene glycol, i-butylene glycol, n-propylene glycol, 1,4-butanediol, cyclohexanedimethanol, and mixtures thereof. Preferably, the diol in line 370 is ethylene glycol. The diol in conduit 370 is introduced into the liquor removal zone 360 via conduit 370. Removal of contaminated water via conduit 365 in the liquor removal zone 360 can be achieved using a variety of techniques including, but not limited to cyclones, centrifuges, and filters. The key factor in the liquor removal zone 360 is to select a temperature range where the typical contaminants preferably continue to be with the aqueous mother liquor instead of continuing to be with the carboxylic acid. The resulting mixture of carboxylic acid / diol is removed via line 375. The resulting mixture of carboxylic acid / diol in line 375 is suitable as a feedstock for the esterification of the carboxylic acid with the diol to produce the carboxylic acid ester. In a seventh embodiment of this invention, a process for producing a terephthalic acid / diol mixture comprises removing a portion of water contaminated with p-toluidic in an aqueous mixture of terephthalic acid by adding a diol in a liquor removal zone to produce said mixture terephthalic acid / diol . The liquor removal zone, the aqueous terephthalic acid mixture and a process for producing the aqueous mixture are subsequently described in an eighth embodiment of the invention. In the eighth embodiment of this invention, a process for producing a terephthalic acid / diol mixture is provided as shown in Figure # 4. Step (1) comprises mixing a crude terephthalic acid powder in line 405 with water in line 415 in a mixing zone 410 to form a crude terephthalic acid solution in line 420. The mixture of the raw terephthalic powder in line 405 with water in line 415 in the mixing zone 410 can be achieved by any means known in the art. The initial feed material is the crude terephthalic acid powder in line 405. The total amount of p-toluidic acid 4-carboxybenzaldehyde in the crude terephthalic acid powder in line 405 is less than 6000 ppm in basis weight. Another feature of the terephthalic raw powder 405 is the color as measured by b * is less than 7. Preferably the color measured by b * is between 4 and 6. This crude terephthalic acid powder in line 405 is introduced into a mixing zone 410. The mixing zone 410 can be any container or equipment capable of mixing the crude terephthalic acid powder in conduit 405 with water in conduit 415. The crude terephthalic acid powder and water are heated to a temperature of 230 ° C or higher to dissolve the crude terephthalic acid powder in conduit 405 in the mixing zone 410 to produce the crude terephthalic acid solution in conduit 420. Preferably, the crude terephthalic acid solution in the mixing zone 410 is heated to a temperature in the range from 240 ° C to 300 ° C. The pressure of the mixing zone 410 is 900 psia to 1400 psia to dissolve the crude terephthalic acid powder in the conduit 405 in the mixing zone 410. Generally, the concentration of crude terephthalic acid powder 405 in the crude solution terephthalic acid 402 is in a range of 15% to 35% by weight, preferably 20 to 30% by weight. Step (2) The crude solution of terephthalic acid in dye 420 is decolorized in an area of the reactor 425 to form a decolorized solution of terephthalic acid in line 435. The decolorization of the crude solution of carboxylic acid in line 420 can be achieved by any means known in the art. Preferably, the decolorization can be achieved by reaction of the crude carboxylic acid solution in line 420 with hydrogen in line 430 in the presence of a catalyst in a zone of reactor 425 to produce a decolorized carboxylic acid solution. For reactor zone 425, there are no special limitations in the form or construction of these, subject to an arrangement that allows hydrogen to be supplied in conduit 430 to contact the crude terephthalic mixture 420 with the catalyst in the reactor zone . The catalyst is usually a single metal of Group VIII or combination of Group VIII metals. Preferably, the catalyst is selected from a group consisting of palladium, ruthenium, rhodium and combinations thereof. More preferably, the catalyst is palladium. Typically, the catalyst is preferably supported on porous carbon. Reactor zone 425 comprises a hydrogenation reactor which operates at a temperature of 230 ° C or higher. Preferably the hydrogenation reactor operates in the range of 240 ° C to 300 ° C. The hydrogenation reactor operates at a pressure of 900 psia at 1400 psia and at a hydrogen partial pressure of at least 100 psi. Preferably, the partial pressure of hydrogen is in the range of 100 to 300 psia. By hydrogenation treatment, characteristically yellow compounds in the crude solution of terephthalic acid 420 are converted to colorless derivatives. In addition, the reactor zone converts a portion of 4-carboxybenzaldehydes to p-toluidic acid. The hydrogen in line 430 is fed at a rate of at least 1.5 times the molar ratio necessary to convert the 4-carboxybenzaldehyde in the crude terephthalic mixture 420 to p-toluidic acid. Preferably the hydrogen 430 is fed at a rate of at least 2.0 times the molar ratio necessary to convert the 4-carboxybenzaldehyde in the crude terephthalic mixture 420 to p-toluidic acid. The color b * is between 0.5 to 4 in the decolorized solution of terephthalic acid in conduit 435. Preferably the color b * of the terephthalic acid solution in conduit 435 is between 0.5 to 2. More preferably the color b * in the solution decolorized terephthalic acid in conduit 435 is between 0.5 to 1.5. Step (3) comprises crystallizing said terephthalic acid solution in conduit 435 in a crystallization zone 445 to form a mixture of aqueous terephthalic acid in conduit 455. The crystallization zone 445 comprises a container or plurality of vessels capable of removing water via the duct 450 of the decolorized terephthalic acid solution in line 435 to produce an aqueous mixture of terephthalic acid in line 455. Typically, the containers comprise at least one crystallizer as previously described. Generally, the aqueous mixture of terephthalic acid in line 455 has a terephthalic acid concentration of from 10 to 60 weight percent, preferably 20 to 40 weight percent. Examples of such systems can be found in U.S. patents. 5,567,842 and 3,931,305 both of which are incorporated herein by reference. The temperature range of the aqueous mixture of terephthalic acid in line 455 is 120 ° C to 270 ° C. The pressure range of the crystallization is from 75 to 1400 psia. Step (4) comprises removing a portion of water contaminated with p-toluidic acid via line 465 in the aqueous mixture of terephthalic acid 455 by addition of a diol in line 470 in a liquor removal zone 460 to produce the mixture of terephthalic acid / diol in line 475. The purpose of the liquor removal zone 460 is to replace the water contaminated with p-toluidic acid with a diol in line 470. The diol in line 470 is selected from a consistent group of ethylene glycol, diethylene glycol, n-butylene glycol, i-butylene glycol, n-propylene glycol, 1,4-butanediol, cyclo-hexanedimethanol, and mixtures thereof. Preferably, the diol in line 470 is ethylene glycol. The diol in line 470 is introduced into the liquor removal zone 460 via line 470. Removal of contaminated water from p-toluidic acid via line 465 in the liquor removal zone 460 can be achieved using a variety of techniques including, but not limited to, cyclones, centrifugation, and filtration. The main factor in the liquor removal zone 460 is to select a temperature range in which the p-toluidic acid and 4-carboxybenzaldehyde will preferably be continued with the aqueous mother liquor instead of continuing to continue with the terephthalic acid. The liquor removal zone 460 operates at a range of 120 ° C to 270 ° C / preferably in the range of 120 ° C to 150 ° C. Water contaminated with p-toluidic acid is removed via conduit 465. The resulting mixture terephthalic acid / diol on cellduct 475 is suitable as a feedstock for the esterification of terephthalic acid with a diol to produce the terephthalic acid ester. It is noted that in relation to this date, the best method known by the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims

CLAIMS 1. - A process for producing a carboxylic acid / diol mixture, characterized by the addition of a diol to a decolorized solution of carboxylic acid in an esterification zone of the reactor to remove a portion of the water to form the carboxylic acid / diol mixture.; wherein the carboxylic acid and diol subsequently react in said esterification zone to form a hydroxyalkyl ester stream. 2. - A process according to claim 1 characterized in that the carboxylic acid is selected from a group consisting of terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, and mixtures thereof. 3. A process for producing a carboxylic acid / diol mixture, characterized in that it comprises the following steps: (a) mixing a crude carboxylic acid powder with water in a mixing zone to form a crude solution of carboxylic acid; wherein the carboxylic acid is selected from a group consisting of terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, and mixtures thereof; (b) decolorizing the crude carboxylic acid solution in a zone of the reactor to produce a decolorized solution of carboxylic acid; (c) optionally, vaporizing the decolorized carboxylic acid solution in a vaporization zone to remove a portion of water from the decolorized carboxylic acid solution; and (d) adding a diol to the decolorized carboxylic acid solution in an esterification zone of the reactor to remove a portion of the water to form the carboxylic acid / diol mixture; wherein the carboxylic acid and diol subsequently react in the esterification zone to form a hydroxyalkyl ester stream. . A process for producing a mixture of tephthalic acid / diol, characterized in that it comprises adding a diol to the decolorized solution of terephthalic acid in an esterification zone of the reactor to remove a portion of the water to form the mixture terephthalic acid / diol; wherein the terephthalic acid and diol subsequently react in the esterification zone to form a hydroxyalkyl ester stream. 5. - A process for producing a terephthalic acid / diol mixture, characterized in that it comprises the following steps: (a) mixing a powder of crude terephthalic acid with water in a mixing zone to form a crude solution of terephthalic acid; (b) decolorizing the crude solution of terephthalic acid in a zone of the reactor to form a decolorized solution of terephthalic acid; (c) optionally, vaporizing the decolorized terephthalic acid solution in a vaporization zone to remove a portion of the water from the decolorized terephthalic acid solution; and (d) adding a diol to the decolorized terephthalic acid solution in a striation zone of the reactor to remove a portion of the water to form the terephthalic acid / diol mixture; wherein the terephthalic acid and diol subsequently react in the esterification zone to form a hydroxyalkyl ester stream. 6. - A process according to claim 5 characterized in that the decolorization is achieved by the reaction of the crude solution of terephthalic acid with hydrogen in the presence of a catalyst in the reactor zone to produce a decolorized solution of carboxylic acid. 7. - A process according to claim 5 characterized in that the crude terephthalic acid powder contains a concentration of p-toluidic acid and 4-carboxybenzaldehyde less than 900 ppm by weight. 8. - A process according to claim 5 characterized in that the vaporization occurs at a pressure between 75 psia to 1400 psia, and a temperature greater than 150 ° C. 9. - A process according to claim 5 characterized in that the addition occurs at a temperature higher than 240 ° C and a pressure between 40 psia to 100 psia. 10. - A process according to claim 5 characterized in that the diol is introduced into the esterification zone of the reactor at a temperature between 150 ° C to 300 ° C. 11. - A decolorized solution of terephthalic acid produced by the process of claim 5. 12. - A process for producing a carboxylic acid / diol mixture, characterized in that it comprises removing a portion of water contaminated with p-toluene in an aqueous mixture by adding a diol in a liquor removal zone to produce the carboxylic acid / ethylene glycol mixture. 13. - A process for producing a carboxylic acid / diol mixture, characterized in that it comprises the following steps: (a) mixing a crude carboxylic acid powder with water in a mixing zone to form a crude solution of carboxylic acid, - (b) ) decolorizing the crude carboxylic acid solution in a zone of the reactor to form a decolorized carboxylic acid solution, - (c) crystallizing the decolorized carboxylic acid solution in a crystallization zone to form an aqueous mixture; and (d) removing a portion of the contaminated water in the aqueous mixture by adding a diol in a liquor removal zone to produce the carboxylic acid / diol mixture. 14. - A process according to claim 3 or 13 characterized in that the decolorization is achieved by the reaction of the crude carboxylic acid solution with hydrogen in the presence of a catalyst in the reactor zone to produce a decolorized carboxylic acid solution. 15. - A process according to claim 13 characterized in that the concentration of the crude carboxylic acid in the raw solution of carboxylic acid is in the range of between 15% to 35% by weight. 16. A process according to claim 14 characterized in that the reaction occurs at a sufficient hydrogen ratio to produce a decolorized solution of carboxylic acid with a color b * between 0.5 to 4. 17. - A process for producing a mixture of terephtlic acid / diol, characterized in that it comprises removing a portion of water contaminated with p-toluidic acid in an aqueous mixture of terephthalic acid by the addition of a diol in a liquor removal zone to produce said mixture terephthalic acid / diol. 18. - A process for producing a terephthalic acid / diol mixture, characterized in that it comprises the following steps: (a) mixing a crude terephthalic powder with water in a mixing zone to form a crude terephthalic acid solution; (b) decolorizing the crude solution of terephthalic acid in a zone of the reactor to form a decolorized solution of terephthalic acid; (c) crystallizing the decolorized terephthalic acid solution in a crystallization zone to remove a portion of water from the decolorized terephthalic acid solution to form an aqueous mixture of terephthalic acid; and (d) removing a portion of water contaminated with p-toluidic acid in the aqueous mixture of terephthalic acid by adding a diol in a liquor removal zone to produce said mixture terephthalic acid / diol. 19. - A process according to claim 18 characterized in that the decolorization is achieved by the reaction of the crude solution of terephthalic acid with hydrogen in the presence of a catalyst in the reactor zone to produce a decolorized solution of carboxylic acid. 20. - A process according to claim 18 characterized in that the crude terephthalic acid powder contains a total concentration of p-toluidic acid and 4-carboxybenzaldehyde less than 6000 ppm by weight. 21. - A process according to claims 1, 3, 4, 5, 12, 13, 17 or 18 characterized by the diol is selected from the group consisting of ethylene glycol, diethylene glycol, n-butylene glycol, i-butylene glycol, n-propylene glycol , 1,4-butanediol, cyclohexanedimethanol, and mixtures thereof. 22. - A process according to claim 5 or 18 characterized in that the raw terephthalic acid powder has a color b * of less than 7. 23. - A process according to claim 5 or 18 characterized in that the mixing occurs at a pressure of between 900 psia to 1400 psia. 24. - A process according to claim 5 or 18 characterized in that the concentration of said crude terephthalic acid in the crude solution of terephthalic acid is in the range of between 15% to 35% by weight. 25. - A process according to claim 6 or 19 characterized in that the reaction occurs at a temperature greater than 230 ° C and a pressure between 900 psia and 1400 psia. 26. - A process according to claim 6 or 19 characterized in that the reaction occurs at a hydrogen flow rate of 1.5 times the molar ratio necessary to convert 4-carboxybenzaldehyde of p-toluidic acid into said terephthalic solution. 27. - A process according to claim 6, 14 or 19, characterized in that the catalyst in the reactor zone comprises a Group VIII metal or combinations thereof. 28. - A process according to claim 18 characterized in that the crystallization occurs at a temperature higher than 150 ° C and at a pressure of between 75 psia at 1400 psia. 29. - A process according to claim 18 characterized in that the addition of said diol occurs at a temperature between 120 ° C to 270 ° C. 30. A process according to claim 18, characterized in that the diol is introduced into the liquor removal zone at a temperature between 150 ° C to 300 ° C. 31. - A process according to claim 13 or 18 characterized in that the liquor removal zone comprises at least one device selected from the group consisting of a cyclone, a filter, and a centrifuge. 32. - A process according to claim 18 characterized in that the aqueous solution of terephthalic acid has a terephthalic acid concentration between 20% to 60% by weight. 33. - A mixture of aqueous terephthalic acid produced by the process of claim 18. 34. An aqueous mixture of terephthalic acid characterized by terephthalic acid in the range from 10 to 40% by weight, water in the range of 60 to 90% by weight, and decolorized bodies in which the total of decolorized bodies in the composition is less than 200 ppm; wherein the decolorized bodies comprise fluoranodicarboxylic acid. 35. A process for the manufacture of a hydroxyalkyl ester stream characterized in that it comprises adding a diol to an aqueous mixture of terephthalic acid to form a terephthalic acid / diol mixture comprising terephthalic acid diol and water, in which the amount of terephthalic acid is greater than 40% by weight, in which the molar ratio of water to diol ranges is from 0.01: 1 to 1.5: 1. 36. A hydroxyalkyl ester obtained by introducing a diol into an esterification zone containing a mixture comprising an aqueous mixture of terephthalic acid. 37. - A process for producing a carboxylic acid / diol mixture of crude carboxylic acid powder without isolation of a substantially dry solid of carboxylic acid. 38. - A process for producing a crude terephthalic acid / diol mixture of crude terephthalic acid in powder form without isolation of a substantially dry solid of terephthalic acid.